Vehicle headlamps are placed as low as possible so that glare from oncoming vehicles is minimized. Light beams from headlamps can not however be directed too low because light that is reflected, especially from a wet road surface, causes glare to the eyes of the driver of an oncoming vehicle. Also fog, rain or snowfall that is illuminated by the headlamps of a vehicle may reduce visibility. In this case, light is reflected from raindrops or snowflakes to the eyes of the driver and prevents him from seeing far-away objects on the road.
Presently headlamps of vehicles are structurally alike and function according to the same principle. Typically they have a housing with a light bulb, reflector and protective glass. The bulb of the headlamp has two filaments, one of them, a filament for distant lights, is disposed at the focus of a parabolic mirror surface and, in a corresponding way, the others a filament for dip lights, is disposed a few millimeters in front of the focus. All light beams of the distant light, which come from the focus, are reflected by the mirror surface in a direction parallel with the focal axis. In a corresponding way, all beams of the dip light, which come from the front of the focus, are reflected downwards towards the focal axis.
The function of the protective glass is to serve as a diffusor for the thin light cone that comes from the reflector so that one obtains a desired light distribution. Therefore, the protective glass is provided with different kinds of grooves which cause the light cone to spread. The housing is either spherical or, depending on the motorcar, rectangular or has some other form. The design of present motorcars requires a broad and flat shape of the headlamp.
Headlights which have a sealed structure are also used as headlamps. The sealed housing is filled with gas and and the filaments are free. These, so-called Sealed-Beam lights, are used especially in the United States, UK and Japan.
Conventional headlamps have following drawbacks which are due to their structure and their principle of operation. The metal coating of the mirror surface on the inner surface of the housing is continuously exposed to air. This leads to gradual darkening of the metal coating and reduction in the luminous efficiency of the headlamp. For instance, humidity and impurities penetrate into the housing through an opening which is used for installing the bulb. Also, the headlamp is easily broken. For instance, one hit of a stone can break the headlamp so that it can not be used anymore. Furthermore possiblities to change direction of the light cone are limited. Additionally changing of the direction of the light by means of the protective glass is difficult and impractical because scattering, energy losses and glare, always takes place within the glass-air boundary surface.
The German Offennlegungsschrift 3 542 292 presents a signal lamp for a vehicle. The lamp comprises an elongated body made of a solid material. The front surface of the body forms the light transmittal surface of the lamp and the rear surface is provided with V-shaped grooves. The side of the V shaped grooves facing the light source is made light reflecting, thus forming a mirror surface. Light coming from the source along the body is reflected by the mirror surface. The reflected light then proceeds through the light transmitting surface.
There are drawbacks with this kind of lamp. It is difficult to shape the lamp so that the light transmitting surface can be brought downwardly near the road surface. It is also difficult to produce a headlamp that would make changing of the direction of the front light possible